3. Combine remaining 1/4 teaspoon salt, pepper, and lamb in a large bowl. Divide lamb mixture into 8 equal portions; shape each into a 1/2-inch-thick patty. Place patties on the rack of a broiler pan coated with cooking spray; place rack in pan. Broil 6 minutes, turning once after 3 minutes. Remove from oven; let stand 3 minutes.

4. Broil buns, cut sides up, 2 minutes or until lightly toasted. Place patties on bottom halves of buns; top each patty with about 1 1/2 tablespoons caramelized onion and about 3/4 teaspoon blue cheese. Cover with top halves of buns.